diff --git a/accessible/windows/msaa/Platform.cpp b/accessible/windows/msaa/Platform.cpp
index b2b0aa54558a1855230fe4eca471779485339b82..65b33102f3ef7450b8c45401ed594145fd4cb393 100644
--- a/accessible/windows/msaa/Platform.cpp
+++ b/accessible/windows/msaa/Platform.cpp
@@ -49,6 +49,10 @@ a11y::ProxyDestroyed(ProxyAccessible* aProxy)
 {
   ProxyAccessibleWrap* wrapper =
     reinterpret_cast<ProxyAccessibleWrap*>(aProxy->GetWrapper());
+  MOZ_ASSERT(wrapper);
+  if (!wrapper)
+    return;
+
   wrapper->Shutdown();
   aProxy->SetWrapper(0);
   wrapper->Release();